1. Field of the Invention
The present invention relates to instrument mounting assemblies and particularly to a panhead assembly for mounting instruments of the type designed for control about a vertical axis or a horizontal axis, such as a camera during panning or tilting.
This invention relates more particularly to a drag mechanism for such panheads as well as an adjustable loading system to permit a given panhead to accommodate different instruments within a range of weights.
An instrument panhead is that structure mounted between a stationary base and an instrument such as a camera which gives the instrument user the ability to tilt and pan the instrument about horizontal and vertical axes respectively. Panheads, particularly those intended for moving cameras, usually embody a drag mechanism to create an artificial resistance to instrument movement which, desirably, is both adjustable and constant. The effect is to obtain smooth, uniform rotation about the panhead axes at a rate dependent upon the direction and amount of force exerted by the instrument user.
Another problem related to optical instruments, such as cameras mounted on a panhead, is created by the shifting of the center of gravity of the camera during tilting, that is, rotation of the instrument with respect to a horizontal axis. The problem is especially troublesome when the camera is mounted above the panhead when the center of gravity of the instrument is displaced from a vertical line passing through the axis of rotation, thus creating a moment arm on one side or the other of the vertical axis during the tilting.
2. Description of the Prior Art
Various type drag mechanisms have been employed in an effort to create an artificial resistance to panning or tilting of the camera in order to provide a uniform movement of the instrument, notwithstanding erratic movements on the part of the operator. An early method employed, utilized cork covered brake shoes operating in an extremely viscous fluid within a brake drum, the spacing of the brake shoes being adjustable. This drag mechanism is shown in U.S. Pat. No. 2,998,953 entitled "Panhead", issued on Sept. 5, 1961, to O'Connor. This particular patent also showed a structure for overcoming the problem related to the weight shifting of the camera during the tilting operation by employing a pair of coil springs, one clockwise and one counter-clockwise, secured to the shaft defining the horizontal axis, the springs operating against each other to counterbalance the camera.
Another panhead drag mechanism is shown and described in U.S. Pat. No. 3,822,769 entitled "Panhead Drag Mechanism" issued to O'Connor on July 9, 1974, a mechanism utilizing a stack of drag plates mounted to slide into interleaved relationship with a plurality of discs fixed perpendicularly on the shaft. Similar discs and drag plates are utilized for the panning drag mechanism as well as the tilting drag mechanism.
U.S. Pat. No. 3,180,603 issued to O'Connor on Apr. 27, 1965, entitled "Instrument Supporting Head" shows a structure designed to circumvent the problem associated with the weight shifting of the camera by providing an offset platform, vertically positionable to a point where the center of gravity of the camera can be made to substantially coincide with the axis of rotation of the horizontal, or tilting, shaft. This patent also shows another type of drag mechanism.
Each of the preceding drag mechanisms requires, for its operation that surfaces such as plates or brake shoes, be in proximate relationship. Plates and brake shoes are essentially friction surfaces suitably arranged to provide the necessary drag force.
Although all the mechansims described in the preceding patents are suitable for the intended purpose, the requirements for various panhead mechanisms in large part will be determined by the instrument with which they are to be used and the application to which they are to be put. For cameras within a given weight range, such as 30 to 50 pounds, it is desirable that the panhead be compact and efficient, easily adjustable, and preferably have means for "tuning" the panhead to provide a counterbalance which is adjustable precisely in accordance with the weight of the instrument. For such a compact panhead it is likewise desirable to have the drag mechanism relatively uncomplicated and efficiently packaged in a minimal amount of space.